The preservation of biofilms on macroalgae by osmium vapour

The aims of this study were to determine if osmium vapour treatment prior to glutaraldehyde fixation could preserve the biofilms found on macroalgae and to gain insight into the structure of the extracellular polymeric substance (EPS or slime layer) of the biofilm. The microscopic surface features of twelve different species of macroalgae from Palm Beach, KwaZulu-Natal, South Africa were compared after being subjected to the different fixation procedures. Treating the seaweed samples with osmium tetroxide (OsO4) prior to fixation with glutaraldehyde significantly enhanced the preservation of the EPS of the biofilms. The EPS was found to be complex and multi-layered with two types of EPS being distinguished, a fluffy or downy variety, and a flat sheet-like type, of which the latter varied in thickness.